title: In-vitro strength degradation of dental ceramics and novel PICN material by sharp indentation.
abstract: OBJECTIVE
  To determine the flexural strength and subsequent strength degradation of a range of dental CAD/CAM ceramic materials and novel PICN (Polymer-Infiltrated-Ceramic-Network) materials by means of pre-damaging with Vickers indentations at various loads.
  
  
  METHODS
  The materials tested included (Mark II, PICN test material 1 and 2, In-Ceram Alumina, VM 9, In-Ceram YZ; Vita Zahnfabrik, Bad Saeckingen, Germany) and (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein). Bending bars were cut and lapped with 15 µm diamond suspension. Initial flexural strength (n=10) was determined in three-point-bending. To evaluate the damage tolerance, Vickers indentations were placed on the bending bars (n=35) with varying loads (1.96-98.07 N). The indented bending bars were subsequently loaded to fracture in three-point-bending. In addition, the fracture toughness was determined by the indentation strength (IS) and the SEVNB technique (n=5).
  
  
  RESULTS
  With increasing indentation loads the fracture strength of all materials tested decreased. The material with the highest fracture resistance to indentation induced damage, was the PICN test material 1 with an indentation load-flexural strength curve slope of 0.21. In-Ceram YZ exhibited the highest damage susceptibility with a slope of 0.4. The fracture toughness varied with the measurement technique and material in the range of 0.82 (VM 9) to 4.94 (In-Ceram YZ) MPa√m for the SEVNB method and 0.96 (VM 9) to 4.97 (In-Ceram YZ) MPa√m for the IS method respectively.
  
  
  CONCLUSIONS
  This study aims to indicate the likely clinical behavior by evaluating the damage tolerance and R-curve behavior of dental ceramics by in-vitro strength degradation and fracture toughness measurements.
authors.affiliation: Department of Oral Sciences, School of Dentistry, P.O. Box 647, Dunedin 9001, New Zealand. a.coldea@vita-zahnfabrik.com
authors.forename: Andrea
authors.initials: A
authors.lastname: Coldea
authors.forename: Michael V
authors.initials: MV
authors.lastname: Swain
authors.forename: Norbert
authors.initials: N
authors.lastname: Thiel
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D006244:Hardness; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry*
chemical_list: D003764:Dental Materials; D011108:Polymers
keywords: Damage tolerance; Dental ceramics; Flexural strength; Fracture toughness; Interpenetrating phase composite; Strength degradation; Vickers indentation